This invention relates to a system for coding an article using a microparticle taggant system and to products marked therewith.
Manufacturers of materials which are shipped in bulk and can be easily confused, such as chemicals, paints, oils, plastics, pigments, clays, fertilizers and explosives, have desired methods for identifying samples of their product, for example, to determine its corresponding shipment or manufacturing lot number, or to determine its particular date and method of manufacture, packing, shipment, etc.
A variety of methods are available for marking bulk materials. For example, U.S. Pat. No. 1,787,995 describes a method for identifying lubricating oil by adding small markers such as letters, initials or arbitrary symbols of about the same specific gravity as the lubricating oil to the oil.
U.S. Pat. No. 4,053,433 describes a method of marking a substance with microparticles which are encoded with an orderly sequence of visually distinguishable colored segments that can be detected with a microscope or other magnifying device.
GB 1568699 describes systems for making microparticles of layered colored material, which have generally parallel flat surfaces at the extremities of the code with irregular broken edges therebetween, allowing for visualization of the code. Incorporation of the microparticles in a clear lacquer is disclosed as a method for applying the microparticles to objects.
DE 19614174 describes a process for producing multilayered microparticles by forming a laminate sheet of colored layers and crushing the sheet. The individual marking layers are applied by a printing process, by bronzing, by spray painting or by roll coating.
U.S. Pat. No. 4,606,927 describes microparticle taggants encased in a transparent solid matrix obtained by hardening a liquid adhesive.
Since the late 1970""s, color-coded micro-particles have been on the market for the purpose of covertly tagging materials and finished goods. These particle systems are still in use today and have been modeled after the color-coding scheme used for many years on electrical resistors. By assigning numeric values to colors, and placing the colors in layers next to each other, numeric information can be encoded into particles of various sizes. The common color scheme used has been the decimal values 0 through 9 represented by black, brown, red, orange, yellow, green, blue, violet, gray, and white respectively.
Microtrace, a Minnesota company, uses colored plastic particles to mark materials such as explosives and consumer objects. The basis of their coding system is the layering of colors in those particles, where the order of the different colors creates a number using the color code scheme found on common electrical resistors, with some adjustments as discussed below.
To use such a system where the colored layers must be read in a specific order, there must be some means of indicating the particle orientation, i.e. which observed layer has the least value and which numeric places the other layers represent. This has been achieved through the use of a black xe2x80x9cdatumxe2x80x9d layer. The datum layer indicates that the layer adjacent to it is the lowest value numeric place, with subsequent layers representing increasingly higher numeric places. For example, if a coded particle has black, red, green, yellow, and orange layers respectively, the black layer indicates that the red layer is in the lowest numeric place. Thus, given the common scheme described above, the numeric code is 2 plus 50 plus 400 plus 3000, representing a decimal value of 3452.
One of the drawbacks of this approach is that using one of the numeric value indicators for the datum means that the adjacent layer can never have that value. In this case, the lowest numeric place, represented by the second layer, can never have the value of zero. This eliminates 10 percent of the available numeric codes, dropping the first numeric place from base 10 to base 9. Likewise, each of the other layers cannot use colors when they are used in adjacent layers dropping them, as well, from base 10 to base 9. Thus, a five-layer particle, using 10 colors as value indicators, will yield 94=6561 numeric codes, and a 7-layered particle will yield 96=531,441 numeric codes.
To partially remedy the problems associated with having a limited number of codes and the limitations of slow code formulation, providers of the scheme described will sell the same codes to multiple buyers, differentiating them by a xe2x80x9ccorporate code.xe2x80x9d The corporate code is represented by 3 layers, such as red/black/red for a first customer, and is unique to each customer. However, numeric xe2x80x9csub-codesxe2x80x9d of a higher number of layers are commonly provided to many customers. Consequently, when a sub-code is supplied to another customer containing a corporate code sequence anywhere in the number, e.g., in the sequence red/black/red/yellow/red, particle fragments can be can be produced which may be misread as the first customer""s corporate code.
Microparticle taggants potentially can be used for identifying many types of materials or objects, including bulk materials (e.g., fertilizer, chemicals, paints, oils, plastics, pigments, clays, fertilizers, explosives, etc.), prepackaged materials (e.g., shampoo, conditioner, lotion, motor oils, pharmaceuticals, etc.) and individual product units (e.g. stereos, cameras, computers, VCRs, furniture, motorized vehicles, livestock, etc.). This potential, however, has not been widely realized, at least in part due to the large expense in manufacturing uniquely coded particles.
A need exists therefore for a microparticle taggant system that will allow practical code-formulation, while maximizing numeric information and yet be easily understood and utilized by a customer.
The invention in various aspects relates to processes for marking an article by applying thereto a taggant, marking formulations comprising a taggant, and articles marked with a taggant. The taggant comprises a plurality of microparticles having two or more distinguishable marker layers corresponding to a predetermined numeric code.
In one aspect the invention is characterized in that the plurality of particles comprises a plurality of microparticle sets of at least one microparticle, each microparticle set is characterized by a specific marker layer combination different from each other microparticle set, and the combination of microparticle sets employed in said taggant collectively forms the numeric code.
Suitably, the marker layers each comprise a distinguishably different color or color enhancer. In some embodiments, each of the specific marker layer combinations employed in the taggant has the same number of layers and/or each specific marker layer combination employs two or three layers. The taggant may be formulated with a binder, such as an adhesive or coating complace, which fixes the taggant to the object or material.
In some embodiments of the invention, each said specific marker layer combination employs two layers, the numeric code is a binary code having a predetermined number of places and having two values at each place, each microparticle set codes for one said value in a specific place in the code and the absence of said microparticle set in the taggant codes for the other said value at said specific place.
In a further aspect of the invention, the microparticle sets employed in the taggant include at least one datum marker layer, which function to identify an orientation of the value marker layers coded and is also coded to include place information, and at least two value marker layers coded to specify a value within the place, the datum marker layer(s) being readily distinguishable from the value marker layers.
In some embodiments, the present invention enables a full series of contiguous numeric values to be presented in a microparticle taggant without suffering any gaps in the numeric sequence available. This is particularly advantageous where the numeric value codes for a sequential series, such as a date, driver""s license, etc., which cannot be adequately represented with systems containing sequence gaps.